Recent research (Connor, Morrison, &Katch, 2004;Foorman, Francis, Fletcher, Schatschneider, &Mehta, 1998;Juel &Minden-Cupp, 2000) has revealed that the effects of certain types of instruction may depend on the specific oral language and early reading skills that children bring to the classroom. The proposed research seeks to examine the causal implications of these child-by-instruction interactions and their effect on children's reading development To this end, we will implement a program of individualized first grade language arts instruction, based, in part, on children's oral language and reading skills, and examine its efficacy using an experimental design in two waves, including a cluster randomized field trial. In each wave, schools are randomly assigned to treatment and control groups. Schools (n = 12 per wave) and their first grade teachers (n = approximately 22) and students (n = approximately 540) are from school districts with both rural and urban areas that are economically and culturally diverse. The proposed implementation of individualized instruction will be supported in two ways, first through intensive teacher training and, second, through computer-based networked Assessment-to-instruction and Simulated Classroom Interactive Interface (SCII, Connor, 1998) technology and teacher education software, Knowledge Networks on the Web (KNOW, Fishman, Marx, Best, &Tal, 2003). Broadly implemented, individualized instruction has the potential to maximize all students'reading skill growth, to meet the goal of all children reading at or above grade level by the end of first grade, and to improve pre-service and professional development efforts. The technology will offer researchers more sophisticated methods for modeling the role of children's early language and literacy in school success, including effects on instruction, within complex and dynamic classroom systems. Moreover, this investigation will help to elucidate the causal links between instruction and children's oral language and reading growth.